1. Field of the Invention
The present invention relates to a mass spectrometer and a method of mass spectrometry. The preferred embodiment relates to 3D quadrupole ion traps (“QIT”) and Time of Flight (“TOF”) mass analysers.
2. Discussion of the Prior Art
Known 3D (Paul) quadrupole ion trap mass spectrometers comprise a doughnut shaped central ring electrode and two end-cap electrodes. Such known 3D (Paul) quadrupole ion trap mass spectrometers typically have a relatively low resolution and a relatively low mass measurement accuracy when scanning the complete mass range compared with other types of mass spectrometers such as magnetic sector and Time of Flight mass spectrometers. 3D quadrupole ion traps do however exhibit a relatively high sensitivity in both MS and MS/MS modes of operation. One particular problem with 3D quadrupole ion traps is that they suffer from having a relatively limited mass range and exhibit a low mass to charge ratio cut-off limit below which ions cannot be stored within the quadrupole ion trap. In a MS/MS mode of operation only about a 3:1 ratio of parent mass to fragment mass can be stored and recorded.
Orthogonal acceleration Time of Flight mass spectrometers have relatively higher resolving powers and higher mass measurement accuracy for both MS and MS/MS modes. Typically, orthogonal acceleration Time of Flight mass spectrometers are coupled to ion sources which provide a continuous beam of ions. Segments of this continuous ion beam are then orthogonally extracted for subsequent mass analysis. However, about 75% of the ions are not extracted for mass analysis and are thus lost.
It is therefore desired to address the mass range limitation inherent with conventional quadrupole ion traps and to increase the duty cycle of an orthogonal acceleration Time of Flight mass analyser when performing MS and MS/MS experiments.